The subject invention is a toy aircraft which is designed for remote controlled slow flight, indoor or in a small outdoor yard or field. The aerial lifting body is comprised of a series of lightweight planar or thin airfoil surfaces arranged in a radially symmetrical configuration around a central cavity. A preferred embodiment is a diagonal cube. Suspended within the cavity is a thrust generating propeller system which can be regulated remotely so as to change the angle of the thrust vector within the cavity. Lifting, stability, turning, and general control of the direction of motion in flight is accomplished without any formal wings, rudder, tail, or control surfaces.
There has been a great interest recently in indoor toy aircraft which are small in size yet capable of making remote controlled flight (Radio Control Microflight March 2000 publishers Model Airplane News www.rcmicroflight.com). By necessity such aircraft must be lightweight and have a high degree of inherent stability. They also must be compact in size and design. Long extended wings and tail structures can reduce the maneuverability of the aircraft for indoor areas or small outdoor fields. Extended fragile control surfaces are also vulnerable to damage during crashes.
The first technologic objective of the invention is to provide a lightweight toy aircraft which is compact in size and shape, which is relatively crash-proof and contains an enclosed propeller system, is without extended wings or tail, yet which has a high degree of inherent flight stability, and a high degree of lift to sustain flight at low speeds. The second objective is to provide a very slow flight toy aircraft with an extremely low aspect ratio and a large dihedral so as to provide stability in yaw and lateral direction. The third objective is to provide a very slow flying toy aircraft which can be controlled in flight and can be turned in a small radius without loss of altitude, without any moving control surfaces such as rudder, ailerons, elevators or elevons. The fourth objective is to provide very light weight lift generating surfaces which are internally self-braced under tension and compression. The fifth objective is to provide a means of flight direction control using enclosed thrust vectoring control solely within the center enclosed cavity of the aircraft. Thrust vectoring is superior to moveable control surfaces at very low speed. A sixth objective is to provide a thrust vectoring means which uses only one propeller and does not require blade pitch control.
The present radio controlled toy aircraft invention combines a compact lightweight lifting body with a single propeller vector control to achieve stable very slow flight with a high degree of radio control maneuverability in a small flight area.
Conventional control of slow flight aircraft uses large control surfaces such as elevators, rudders and ailerons or elevons. Because of the slow velocity, large area control surfaces are needed in slow flight. In addition, to achieve adequate lift at slow indoor flight velocities, large wing surfaces areas relative to total weight are required.
In the prior art of radio controlled toy aircraft, control of aircraft direction has been achieved without moveable rudder or elevators using multiple independently controlled motors and propellers (Shugo U.S. Pat. No. 5,087,000, Palieri U.S. Pat. No. 3,957,230, Kress U.S. Pat. No. 4,198,779, Yamamoto et al U.S. Pat. No. 4,760,392, Hansen et al U.S. Pat. No. 4,143,307). In such prior art the aircraft has a conventional wing and tail with horizontal and vertical tail or stabilizing wings. Two motor driven propellers at opposite sides of the central fuselage in the prior art are independently controlled to provide a relative difference in thrust velocity. A higher power applied to the propeller on one side causes the wing on that side to rotate toward the center line and to move at a higher velocity compared to the opposite retreating wing side. This results in a bank of the aircraft because the slower moving opposite wing has less lift. Without a separate control surface to attain horizontal and lateral stability, the control of turning using two independent motors and a conventional wing must therefore be done with skill to avoid a downward spiral resulting in a crash. For the prior art this limits the flight performance to gentle slow turns with a required maneuver after the turn to recovery from the bank by increasing power to gain altitude.
In the prior art tailless aircraft have required airfoils which do not have nose-down pitching moment. In a tailless aircraft such moment can not be counteracted by a horizontal tail which is at some distance behind the center of gravity (Lennon Andy, Basics of R/C Model Aircraft Design, Publisher Air Age Inc. 1996 ISBNO-911295-40-2). Highly cambered airfoils, which generate a high maximum lift, are not suitable for tailless aircraft because they have nose down pitching moment. Flat thin airfoils (Ashley H. and Landahl M. Aerodynamics of Wings and Bodies Dover Publications 1965 pgs 81-97), symmetrical airfoils (Eppler 168), or airfoils with a rear reflex (Eppler 184, Eppler 230) are required for tailless aircraft (Lennon, Andy, Basics of R/C Model Aircraft Design, Publisher Air Age Inc. 1996 ISBNO-911295-40-2). However these airfoils may have a lower maximum lift and a lower stall angle. Offsetting the stall angle can be facilitated by increasing the speed or decreasing the aspect ratio, which are both not suitable for an indoor or park-style slow flight toy aircraft. The present invention overcomes these drawbacks of the prior art.
In contrast to the prior art the aircraft of the present invention has the following unique features which combine to achieve the technologic objectives.
A lightweight slow flight lifting body is achieved with a high degree of flight stability, without tail or extended wings, using a series of opposing angled surfaces geometrically arranged around a central cavity (see FIGS. 1-4). The lift surfaces are all angled from the horizontal to achieve large dihedral stability. Opposite angles of the lifting surface panels vectorally cancel out the lift vector directions to achieve high stability.
The lift surface area is high, for the narrow span and volume occupied. The central cavity encloses the power and control pod for air thrust channeling, safety, and crash resistance.
Using only one propeller, with no blade pitch control, and no control surfaces, controlled turning of the aircraft in a small radius at low speed can be achieved without significant induced banking or rolling. The thrust direction is regulated by rotating the motor and the prop thrust angle xcex2 within the cavity of the lifting body (see FIG. 3).
The angle xcex1 of the rotation plane for the prop is at an upward pitch to the horizontal (see FIG. 2), providing an upward thrust vector and a balancing force. This maintains longitudinal stability because the center of gravity (CG) is forward of the aerodynamic center or neutral point of lift. The upward angle xcex1 thrust vector counterbalances the nose down imbalance of the CG being forward of the aerodynamic center. The angle xcex1 can be fixed or adjustable, preferably between 10 and 20 degrees. Increasing the power causes elevation of the flight path. Changing the angle xcex2 of the prop thrust vector (see FIG. 3) causes turning.
Compact Size, light weight and resiliency for a toy aircraft is achieved by using internal tension and compression bracing, and construction materials similar to that used for kites (see FIG. 5). This design also generates a flat thin or thin symmetrical airfoil necessary for a tailless aircraft. Since this is a tailless aircraft, cambered airfoils are not preferred because they exhibit nose-down pitching moment which can""t be counteracted by a tail-moment arm.
An aircraft constructed in accordance with the present invention exhibits the novel and unobvious combination of aerodynamic features set forth below:
1. Very low Span (e.g., 16 in);
2. Very low Aspect Ratio (e.g., 0.44);
3. Wide chord (length) to span (width) ratio (e.g., 1.0 to 0.5);
4. Very low Reynolds number (e.g., 93,600 at sea level);
5. Very low flight speed (e.g., less than 10 mph);
6. Very high dihedral and low center of gravity for extreme lateral stability (e.g., 90 degrees compound opposing angles of lift surfaces as shown in FIGS. 1 and 4);
7. Tailless;
8. No Control Surfaces, no moveable rudder, no elevator, no aileron which are inefficient at very low flight speeds;
9. Wing body lift surfaces surround and enclose Propeller and drive system;
10. Single Propeller Thrust Control: Elevation of flight path and turning (e.g., less than 4 feet radius) controlled by rotation of thrust direction and speed (RPM) regulation of single propeller with fixed pitch.
The design of an aircraft in accordance with the present invention enables steep ascent and descentxe2x80x94the very low Aspect Ratio increases the effective stall angle. This solves the requirement for a symmetrical, flat or reflexed airfoil (these airfoils have no downward pitching moment) for a tailless aircraft. The present design enables narrow flat horizontal turns with a single propeller thrust angle control and no tail or control surfacesxe2x80x94the large dihedral coupled with 45 degree diagonal panels function as rudders achieves spiral stability. The short span of an aircraft constructed in accordance with the present invention combined with the high dihedral minimizes or prevents banking of the flight path during turning.